Network Working Group T. Henderson Internet-Draft The Boeing Company
Expires: May 26, 2007Intended status: Informational P. Nikander Expires: October 11, 2007 Ericsson Research NomadicLab November 22, 2006April 9, 2007 Using HIPthe Host Identity Protocol with Legacy Applications draft-ietf-hip-applications-00.txtdraft-ietf-hip-applications-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 26,October 11, 2007. Copyright Notice Copyright (C) The Internet Society (2006).IETF Trust (2007). Abstract The Host Identity Protocol (HIP) and architecture (HIP)proposes to add a cryptographic name space for network stack names. From an application viewpoint, HIP-enabled systems support a new address family (e.g., AF_HOST),of host identifiers, but it may be a long time until such HIP- aware applications are widely deployed even if host systems are upgraded. This informational document discusses implementation and API issues relating to using HIP in situations in which the system is HIP-aware but the applications are not. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Approaches for supporting legacy applications . . . . . . . . 5 3.1. Using IP addresses in applications . . . . . . . . . . . . 5 3.2. Using DNS to map domain names to HIs . . . . . . . . . . . 6 3.3. Connecting directly to a HIT . . . . . . . . . . . . . 6 3.3. Connecting directly to a HIT. . 8 3.4. Local address management . . . . . . . . . . . . . . . . . 78 4. Security Considerations . . . . . . . . . . . . . . . . . . . 910 5. AcknowledgmentsIANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. Acknowledgments . . . . 10 6. References. . . . . . . . . . . . . . . . . . . 12 7. Informative References . . . . . . . 10. . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 1114 Intellectual Property and Copyright Statements . . . . . . . . . . 1215 1. Introduction The Host Identity Protocol (HIP)  is an experimental effort in the IETF and IRTF to study a new public-key-based name space for use as host identifiers in Internet protocols. Fully deployed, the HIP architecture will permit applications to explicitly request the system to connectsend packets to another named host by expressing a location- independentlocation-independent name of the host when the system call to connectsend packets is performed. However, there will be a transition period during which systems become HIP-enabled but applications are not. When applications and systems are both HIP-aware, the coordination between the application and the system can be straightforward. For example, using the terminology of the widely used sockets API,Application Programming Interface (API), the application can issue a system call to connectsend packets to another host by naming it explicitly, and the system can perform the necessary name- to-addressname-to-address mapping to assign appropriate routable addresses to the packets. To enable this, a new address family (e.g., AF_HOST)for hosts could be defined, and additional API extensions could be defined (such as allowing IP addresses to be passed in the system call, along with the host name, as hints of where to initially try to reach the host). This note does not define a native HIP API such as described above. Rather, this note is concerned with the scenario in which the application is not HIP-aware and a traditional IP-address-based API is used by the application. To use HIP in such a situation, there are a few basic possibilities: i) allow applications to use IP addresses as before, and provide a mapping from IP address to host identityidentifier (and back to IP address) within the system, ii) take advantage of domain name resolution to provide the application with either an alias for the host identifier or (in the case of IPv6) the host identity tag (HIT) itself, and iii) support the use of HITs directly (without prior DNS resolution) in place of IPv6 addresses. This note describes several variations of the above strategies and suggests some pros and cons to each approach. When HITs are used (rather than IP addresses) as peer names at the system API,API level, they can provide a type of "channel binding" (Section 1.1.6 of ) in that the ESP association formed by HIP is cryptographically bound to the name (HIT) invoked by the calling application. 2. Terminology Host Identity: An abstract concept applied to a computing platform. Host Identifier (HI): A public key of an asymmetric key pair used as a name for a Host Identity. More details are available in . Host Identity Tag:Tag (HIT): A 128-bit quantity formed bycomposed with the hash of a Host Identity. More details are available in  and . Local Scope Identifier:Identifier (LSI): A 32- or 128-bit quantity locally representing the Host Identity at the IPv4 or IPv6 API. Referral: An event when the application passes what it believes to be an IP address to another application instance on another host, within its application data stream. An example is the FTP PORT command. Resolver: The system function used by applications to resolve domain names to IP addresses. 3. Approaches for supporting legacy applications This section provides examples of how legacy applications, using legacy APIs, can operate over a HIP-enabled system and use HIP. The examples are organized by the name used by an application (or application user) to name the peer system: an IP address, a domain name, or a HIT. Finally, some local address management issues are discussed. While the text below concentrates on the use of the sockets connect system call, the same argument canis also be applied to datagram-basedvalid for other system calls.calls using socket addresses. Recent work in the shim6 group has categorized the ways in which current applications use IP addresses .. These uses include short- lived local handles, long-lived application associations, callbacks, referrals, and identity comparisons. Each of the below mechanisms has implications on these different uses of IP addresses by legacy applications. 3.1. Using IP addresses in applications Consider the case in which an application issues a "connect(ip)" system call to connectset the default destination to a system named by address "ip", but for which we would like to enable HIP to protect the communications. Since the application or user does not (can not) indicate a desire to use HIP through the standard sockets API, the decision to invoke HIP must be done on the basis of host policy. For example, if an IPsec- likeIPsec-like implementation of HIP is being used, a policy may be entered into the security policy database that mandates to use or try HIP based on a match on the source or destination IP address, or other factors. The mapping of IP address to host identityidentifier may be implemented by modifying the host operating system or by wrapping the existings sockets API, such as in the TESLA approach .. There are a number of ways that HIP could be used in such a scenario. Manual configuration: Pre-existing SAs may be available due to previous administrative action. Opportunistically: The system could send an I1 to the Responder with an empty value for Responder HIT. Using DNS:DNS to map IP addresses to HIs: If the responder has host identitiesidentifiers registered in the forward DNS zone and has a PTR record in the reverse zone, the initiating system could perform a reverse+forward lookup to learn the HIT associated with the address. Alternatively, the HIT could be stored in some type of HIP name service such as a DHT,distributed hash table (DHT), keyed by IP address. Unless secured with DNSSEC,DNS security extensions, the use of the reverse DNS map is subject to well-known security limitations (an attacker may cause an incorrect IP address to FQDNdomain name binding to occur). These types of solutions have the benefit of better supporting applications that use IP addresses for long-lived application associations, callbacks, and referrals. They have weaker security properties than the approaches outlined in Section 3.2 and Section 3.3, however, because the binding between host identityidentifier and address is weak and not visible to the application or user. In fact, the semantics of the application's "connect(ip)" call may be interpreted as "connect me to the system reachable at IP address ip" but perhaps no stronger semantics than that. HIP can be used in this case to provide perfect forward secrecy and authentication, but not to strongly authenticate the peer at the onset of communications. DNS with DNSSEC,security extensions (DNSSEC) , if trusted, may be able to provide some additional initial authentication, but at a cost of initial resolution latency. Note that this usage does not necessarily reveal to the user of the legacy application that HIP is being used. Using IP addresses at the application layer may not provide the full potential benefits of HIP mobility support. It allows for mobility if one is able to readdress the existing sockets upon a HIP readdress event. However, mobility will break in the connectionless case when an application caches the IP address and repeatedly calls sendto(). 3.2. Using DNS to map domain names to HIs In the previous section, it was pointed out that a HIP-enabled system might make use of DNS to transparently fetch host identifiers prior to the onset of communication. For applications that make use of DNS, the name resolution process is another opportunity to use HIP. If host identitiesidentifiers are bound to domain names (with a trusted DNS) the following are possible: Return HIP LSIs and HITs instead of IP addresses: The system resolver could be configured to return a Local Scope Identifier (LSI) or Host Identity Tag (HIT)HIT rather than an IP address, if HIP information is available in the DNS that binds a particular domain name to a host identity,identifier, and otherwise to return an IP address as usual. The system can then maintain a mapping between LSI and host identityidentifier and perform the appropriate conversion at the system call interface or below. The application uses the LSI or HIT as it would an IP address. Locally use a HIP-specific domain name suffix: One drawback to spoofing the DNS resolution is that some applications actually may want to fetch IP addresses (e.g., diagnostic applications such as ping). One way to provide finer granularity on whether the resolver returns an IP address or an LSI is to distinguish by the presence of a domain name suffix. Specifically, if the application requests to resolve "www.example.com.hip" (or some similar suffix), then the system returns an LSI, while if the application requests to resolve "www.example.com", IP address(es) are returned as usual. Caution against the use of FQDNdomain name suffixes is discussed in .. Since the LSI or HIT is non-routable, a couple of potential hazards arise, in the case of referrals, callbacks, and long-lived application associations. First, applications that perform referrals may pass the LSI to another system that has no system context to resolve the LSI back to a host identityidentifier or an IP address. Note that these are the same type of applications that will likely break if used over certain types of NATs.network address translators (NATs). Second, applications may cache the results of DNS queries for a long time, and it may be hard for a HIP system to determine when to perform garbage collection on the LSI bindings. However, when using HITs, the security of using the HITs for identity comparison may be stronger than in the case of using IP addresses. It may be possible for an LSI or HIT to be routable or resolvable, but such a case may not have the level of security in the binding to host identity that a HIT has with the host identity.either directly or on an overlay. For example, a special IP address that has some location invariance is the identifier-address discussed in . In general, LSIs and HITs considered to date. A term other than LSI may be needed for HIP have been non-routable. 3.3. Connecting directly to a HITthese routable identifiers, since they would no longer be locally scoped. When using DNS, returning a routable identifier would avoid the aforementioned problems with referrals. However, the cost of routability may be that the hash binding between the routable identifier and the host identifier would be weakened, since more bits may be allocated to the hierarchical part. 3.3. Connecting directly to a HIT The previous two sections describe the use of IP addresses and andLSIs as local handles to a host identity.identifier. A third approach, for IPv6 applications, is to configure the application to connect directly to a HIT (e.g., "connect(HIT)" as a socket call). Although more cumbersome for human users (due to the flat HIT name space) than using either IPv6 addresses or domain names, this scenario has stronger security semantics, because the application is asking the system to connectsend packets specifically to the named peer system. Depending on howHITs are ultimately defined, it may be hard for a system to distinguish between a HIT and a routable IPv6 address. Elsewhere it hashave been proposed defined as Overlay Routable Cryptographic Hash Identifiers (ORCHIDs) such that HITsthey cannot be precluded from using highest-ordered bits that correspond to IPv6 addresses, so that at least in the near term, a system could differentiate between a HIT and an IPv6 address by inspection.confused with routable IP addresses; see . Another challenge with this approach is in actually finding the IP addresses to use, based on the HIT. Some type of HIT resolution service would be needed in this case. A third challenge of this approach is in supporting callbacks and referrals to possibly non-HIP-aware hosts. However, since most communications in this case would likely be to other HIP-aware hosts (else the initial connect()HIP associations would fail),fail to establish), the problem may otherwise be instead ifthat the peer host supports HIP but is not able to perform HIT resolution for some reason. 3.4. Local address management The previous sections focused mainly on client behavior (HIP initiator). We must also consider the behavior for servers. Typically, a server may bind to a wildcard IP address and well-known port. In the case of HIP use with legacy server implementations, there are again a few options. As in Section 3.1 above, the system may be configured manually to always, optionally (depending on the client behavior), or never use HIP with a particular service, as a matter of policy, when the server specifies a wildcard (IP) address. When a system API call such as getaddrinfo  is used for resolving local addresses, it may also return HITs or LSIs, if the system has assigned HITs or LSIs to internal virtual interfaces (common in many HIP implementations). The application may use such identifiers as addresses in subsequent socket calls. Some applications may try to bind a socket to a specific local address. If the local address specified is an IP address, again, the underlying system may be configured to still use HIP. If the local address specified is a HIT (Section 3.3), the system should enforce that connections can only come to the specified HIT. If a system has many HITs, an application that binds to a single HIT cannot accept connections to the other HITs in the system. It may be possible for a system to specify a special ORCHID value as a local HIT wildcard value, if such wildcarding among local HIs is desired. When a host has multiple HIs and the socket behavior does not prescribe the use of any particular HI as a source identifier, it is a matter of local policy as to how to select a HI to serve as a source identifier. 4. Security Considerations In this section we discuss the security of the system in general terms, outlining some of the security properties. However, this section is not intended to provide a complete risk analysis. Such an analysis would, in any case, be dependent on the actual application using HIP, and is therefore considered out of scope. The three outlined scenarios differ considerably in their security properties. There are further differences related to whether DNSSEC is used or not, and whether the DNSSEC zones are considered trustworthy enough from an application point of view. When IP addresses are used to represent the peer system, the security properties depend on the the configuration method. With manual configuration, the system'ssecurity of the system is comparable to a non-HIP system with similar IPsec policies. The security semantics of an opportunistic key exchange are roughly equal to current non-secured IP; the exchange is vulnerable to man-in-the-middle attacks. However, the system is less vulnerable to connection hijacking attacks. If the DNS is used, if both maps are secured (or the HITs stored in the reverse MAP)DNS record) and the client trusts the DNSSEC signatures, the system may provide a fairly high security level. However, much depends on the details of the implementation, the security and administrative practises used when signing the DNS zones, and other factors. Using the forward DNS to map a DNSdomain name into an LSI is a case that is closest to the most typical use scenarios today. If DNSSEC is used, the result is fairly similar to the current use of certificates with TLS. If DNSSEC is not used, the result is fairly similar to the current use of plain IP, with the exception that HIP provides protection against connection hijacking attacks. If the application is basing its operations on HITs, the connections become automatically secured due to the implicit channel bindings in HIP. That is, when the application makes a connect(HIT) system call, the resulting connectionpackets will either be connectedsent to a node possessing the corresponding private key or the connection attemptsecurity association will fail.fail to be established. 5. IANA Considerations This document has no actions for IANA. 6. Acknowledgments Jeff Ahrenholz, Gonzalo Camarillo, Alberto Garcia, Miika Komu, Teemu Koponen, Julien Laganier, and Jukka Ylitalo have provided comments on different versions of this draft. 6.7. Informative References  Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-06draft-ietf-hip-base-07 (work in progress), June 2006.February 2007.  Linn, J., "Generic Security Service Application Program Interface Version 2, Update 1", RFC 2743, January 2000.  Nikander, P., "An IPv6 Prefix for Overlay Routable Cryptographic Hash Identifiers (ORCHID)", draft-laganier-ipv6-khi-07 (work in progress), February 2007.  Nordmark, E., "Shim6 Application Referral Issues", draft-ietf-shim6-app-refer-00 (work in progress), July 2005.  Salz, J., Balakrishnan, H., and A. Snoeren, "TESLA: A Transparent, Extensible Session-Layer Architecture for End-to- end Network Services", Proceedings of USENIX Symposium on Internet Technologies and Systems (USITS), Decemberpages 211-224, March 2003.  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005.  Faltstrom, P., "Design Choices When Expanding DNS", draft-iab-dns-choices-04 (work in progress), October 2006.  Bagnulo, M. and E. Nordmark, "Level 3 multihoming shim protocol", draft-ietf-shim6-proto-06draft-ietf-shim6-proto-07 (work in progress), OctoberDecember 2006.  Nikander, P., "An IPv6 Prefix Gilligan, R., Thomson, S., Bound, J., McCann, J., and W. Stevens, "Basic Socket Interface Extensions for Overlay Routable Cryptographic Hash Identifiers (ORCHID)", draft-laganier-ipv6-khi-05 (work in progress), September 2006.IPv6", RFC 3493, February 2003. Authors' Addresses Tom Henderson The Boeing Company P.O. Box 3707 Seattle, WA USA Email: firstname.lastname@example.org Pekka Nikander Ericsson Research NomadicLab JORVAS FIN-02420 FINLAND Phone: +358 9 299 1 Email: email@example.com Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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